1. Field of the Invention
The present invention relates to power supplies. More specifically, the present invention relates to power supplies which include flyback transformers.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Conventional ion and plasma sources typically include a DC actuated gas discharge chamber. Initially, a large voltage is applied to the gas chamber to effect an electron (plasma) discharge from the gas included therein. Prior to the plasma discharge the chamber draws minimal current and appears essentially as an open circuit. Following the plasma discharge the voltage across the chamber substantially decreases and the chamber conducts a relatively high current. It therefore follows that gas discharge chambers included within conventional ion and plasma sources display two distinct sets of electrical characteristics during the course of operation.
The disparity in the electrical parameters of the chamber before and after the initial plasma discharge generally necessitates utilization of a pair of individual power supplies. Specifically, both a high voltage/low current supply and a low voltage/high current supply are initially applied to the chamber. Each of the supplies may be realized, for example, by a conventional pulse width modulated flyback inverter supper. The turns ratio of a transformer included within each of the flyback inverters is appropriately adjusted to yield the desired electrical performance. The high voltage supply is responsible for providing the large voltage required to trigger the initial discharge of electrons within the gas. Following the plasma discharge the high voltage supply is disengaged leaving the low voltage/high current supply to power the chamber throughout steady state operation. In this manner separate power supplies, each designed to meet the power requirements of the gas chamber during a particular interval, are sequentially utilized during chamber operation.
Unfortunately, providing a pair of power supplies for each discharge chamber is generally expensive. Further, considerable complex auxiliary circuitry is required to engage and disengage the separate power supplies in response to the changing electrical characteristics of the discharge chamber. Moreover, during the time period between electron discharge within the chamber and deactivation of the high voltage supply a potentially large current runs through the chamber. The large curring during this transition interval results from the decrease in impedance of the gas chamber following plasma discharge. As a consequence, during the transition inerval the power dissipation of the chamber typically increases substantially. This added power dissipation also stresses the discharge chamber and the components associated therewith. Thus, the employment of a pair of individual power supplies to drive a single gas discharge chamber requires additional control circuitry and is generally expensive and inefficient.
Hence a need in the art exists for a single power supply capable of automatically transitioning between operational modes in responsee to changes in the impedance of a load connected thereto.